In a classic case of "everyone has a twin somewhere", teenager Penrod Schofield runs into trouble when identical but unrelated Danny Dugan moves to town. Danny's dog bites spoiled kid Raymond and and Penrod's dog Duke gets the blame. Penrod and his pals have a junior G-men club and they work to keep Duke away from the authorities. They send Raymond (who is a member of the club, but no longer in good standing) on a wild goose chase involving a messenger pigeon so they can make plans for Duke. Raymond witnesses a deadly payroll heist and is kidnapped by the crooks. He manages to send the boys a clue to where he is being held (by messenger pigeon). Danny joins the gang and together they rescue Raymond and foil the robbers, with Duke playing a heroic role.

Unlike the Parent Trap model Penrod and Danny are played by real life identical twins.